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Title: Scanning tunnelling microscopy study of tuneable metalloprotein conductance
Author: Wrathmell, Claire Louise
ISNI:       0000 0001 3572 9158
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2008
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Azurin wild-type and mutant proteins were directly adsorbed onto pristine gold surfaces. Scanning probe and electrochemical characterisation of the metalloprotein arrays indicated robust, high coverage adsorption with good retention of redox activity. Imaging resolution was optimised through extensive pre-testing of tip and substrate preparations. Tunnelling transport was then examined as a function of environmental conditions (ambient/fluid, bias/set point and temperature). The first documented low temperature protein STM under fluid is presented. The role of azurin's metal centre in the tunnelling pathway was probed using electrochemical STM. Striking differences were observed in the imaging ofredox-active Cu azurin, compared to its redox-inactive Zn analogue. The conductance of Cu azurin was shown to be tunable by the substrate potential at the single molecule level. A peak in molecular contrast was resolved at a potential close to azurin's midpoint potential, with a contrast enhancement of over 55 %. Since the contrast of Zn azurin did not vary as a function of substrate potential, this strongly suggests the involvement of Cu-based densities of states in the tunnelling pathway. Single molecule scanning tunnelling spectroscopy of metalloproteins was demonstrated for the first time. Reproducible negative differential resistance (NDR) features were resolved at positive and negative biases in the 1-V spectroscopy of Cu azurin, but not for Zn azurin. Derivative spectra indicated molecular densities of states involved in Cu azurin's tunnelling pathway. Peak to valley ratios of the Cu azurin NDR features were of the same order of magnitude as the degree of contrast switching observed by ECSTM, suggesting the same redox densities of states were being accessed by both techniques. This work has therefore demonstrated metal centre involvement in tunnel transport across azurin, and shown that the tunnelling conductance can be probed and reversibly tuned at the single molecule level.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available